The invention relates to a coating composition, to a formulation comprising said coating composition, to methods of coating surfaces with the coating composition, and to articles coated with the coating composition. The coating composition is based on a complex of polyelectrolytes and oppositely charged surfactants. The surfactants contain fluorine bonded covalently to carbon atoms. The coating material imparts oleophobic and/or hydrophobic properties to various surfaces. The degree of hydrophobicity and other properties such as, for instance, gas or moisture permeation can be adjusted over a wide range. Through the use of additives, the coating can be executed an a permanent or temporary coating. The readily variable profile of properties, the uncomplicated application, and the low coat thickness result in a wide scope for application as, for example, an antisoiling, antigraffiti or antiadhesion coating.
In the field of coating techniques, there exists a virtually innumerable number of different coating materials, each for very specific applications. In some cases a combination of polyelectrolytes and surfactants has been described.
DE 42 20 975 A1 describes oleophobic and/or permanent hydrophobic finishing for polymeric surfaces with a thin film. The film is formed from at least one layer of a water-soluble polycation and/or of a cationic synthetic resain. To further improve the oleophobic and/or permanently hydrophobic properties, the film may further comprise a long-chain surfactant or an alkyl-substituted polyanion. In the process described, the surface is first treated with a polycation solution and then treated, if desired, with an alkyl-substituted polyanion as second component or with a long-chain surfactant. Therefore, at least two different operations are required for coating. Furthermore, a prerequisite for application of the process is that the surface to be coated possesses a negative zeta potential.
This layer-by-layer construction by adsorption from aqueous solution has already been used for many years for scientific purposes and is described in a review by Decher (Science 277 (1997), 1232-1237).
International Patent Application Wo 96/11981 describes a fluorocarbon-containing additive which is applied subsequently to painted substrates and protects them against soiling or makes them easier to clean. These additives are based on discrete oligomers comprising a polyfunctional oligomeric core to which fluorinated alkyl chains are bonded covalently. The dirt repellency feature is achieved through the fluorinated alkyl chains, while adhesion to the paint is induced by the functionalized core. This type of protection by means of additives is strongly limited to well-defined, i.e. dust-free, painted surfaces. Furthermore, reaction times of from 6 hours to two weeks are necessary for preparing the fluorinated additives.
U.S. Pat. No. 5,330,788 describes a temporary coating for surfaces, developed in particular for protecting automobiles in transit. The coating is based on a film-forming acrylic acid polymer, a nonionic acetylenically unsaturated surfactant, if desired, a phosphate ester surfactant, and a base for neutralization. The coating material can be removed rapidly in contact with a special alkaline aqueous medium, which is likewise described in the patent. Extremely disadvantageous are, apparently, the long drying times for the coating, which are stated as being xe2x80x9covernightxe2x80x9d or 24 hours. Since the principal component, the polyacrylic acid, is a polyelectrolyte which finds application as a super-absorbent (used, for example, in diapers and to improve the water retention capacity of arid soils), it cannot be assumed that these drying times, which are unreasonably long from an economic standpoint, might be substantially reduced.
U.S. Pat. No. 5,387,434 describes an antigraffiti composition whose protective action derives from sodium silicate. Since this is soluble in water, the interface between substrate and environment must be made hydrophobic. This is achieved by means of latex, silicones, or waxes. Particularly suitable are microcrystalline wax emulsions which are stabilized by sodium lignin-sulfonate. Graffiti removal requires high-pressure steam jets with a pressure of 100 psi, and temperatures of up to 90xc2x0 C. Consequently, this process is suitable only for very specific substrates which permit these conditions without damage. No statement concerning the drying time of the coating can be found in the patent. However, it must be assumed that the crosslinking of the silicate requires several hours to days. Furthermore, it is likely that drying, which is retarded as a result of the added wax, will likewise take at least one day under dry conditions.
DE 36 30 520 C1 describes a process for protecting applications of color to surfaces of natural and synthetic stone. The process consists of two steps: first, an inorganic impregnation is applied, which is not specified in any great detail. This is followed by the application of a color-accepting, detachable, wax-like coating which can be removed by means of high-pressure hot water. Owing to the fact that it necessitates at least two different operations, this process is very time-consuming. In the case of typical inorganic impregnations, from at least one to three days are necessary given dry weather. Furthermore, this process is applicable only to a very limited number of specific substrates.
European Patent Application EP 0 695 772 A1 describes a class of fluorine-containing polyethers which are applied to masonry where they crosslink and form an impermeable antigraffiti film. The synthesis of the crosslinkable substances, however, is time-consuming and costly, and the raw material applied requires a drying time of 48 hours on the masonry in order to crosslink sufficiently. Furthermore, the field of use is limited to the coating of masonry.
Available on the market there is a surface protection is system from the company PSS (Protective Surface System) which is based or a polysaccharide mixture. According to an examination certificate from the German Federal Institute of Materials Research (Report No. 3.14.3441-91), effective protection against graffiti with the system PSS 20 requires three coats with drying times of from 24 to 72 hours in each case. Thus from 3 to 9 days are necessary for the application of the protective coat.
All of the abovementioned coating processes are characterized by a closely limited field of use and, in some cases, by drying times of several days for the protective coats.
DE-A-44 28 641 describes mesomorphic complexes comprising anionic polyelectrolytes, cationic polyelectrolytes and/or polyampholytes, and cationic, anionic, nonionic and/or amphoteric surfactants. As a consequence of the mesomorphic structure, generally improved material properties, such as increased mechanical strength, for example, are expected. The materials constructed of these amorphous or mesomorphic polyelectrolytes, such as films or membranes, include as an essential component surfactants having a hydrocarbon framework. Coatings with low-energy surfaces, however, cannot be produced using the fluorine-free complexes described therein.
Antonietti et al. (Adv. Mater. 8 (1996), 41-45) and Lochhaas et al. (Polyelectrolyte-surfactant complexes with fluorinated surfactants: A new type of material for coatings (3rd conference in the series: High Performance Coating Materials, Fluorine in Coatings II, Feb. 24-26, 1997, Munich, Germany) describe complexes comprising cationic polyelectrolytes and anionic fluorinated surfactants. Cationic polyelectrolyte components disclosed include polyacrylic acid, polymethacrylic acid, and poly(diallyldimethylammonium chloride). On contact with moisture these complexes have a very high propensity to absorb water; they swell rapidly and in doing so become soft to gelatinous. This leads to a considerable deterioration in the mechanical properties, so rendering them unsuitable for practical applications as coating material.
It is an object of the present invention to develop a coating material in which at least some of the disadvantages of the prior art are eliminated. In particular, the coating material should be applicable by simple methods to any desired surfaces and should produce a low-energy surface even when small amounts are used. Furthermore, the coating material should be highly stable to a water-containing environment.
This object is achieved through the provision of a coating material based on a complex which comprises at least one nonhygroscopic polyelectrolyte and at least one oppositely charged, fluorinated surfactant.
The coating material of the invention surprisingly allows an accumulation of fluorinated organic groupsxe2x80x94alkyl chains, for examplexe2x80x94at its surface, so that the oleophobicxe2x80x94or hydrophobicxe2x80x94properties of the coated surface are improved. Through the combination of nonhygroscopic polyelectrolyte and fluorinated ionic surfactant a highly ordered, mechanically stable complex is formed which both adheres to almost any substrate and forms a highly fluorinate, low-energy surface. Sufficient adhesion and the formation of low-energy surfaces are inherently contradictory principles, which can surprisingly be unified in one material by the novel combination of nonhygroscopic polyelectrolyte and fluoro surfactant.
The complex of the invention may comprise a cationic polyelectrolyte and an anionic surfactant, or an anionic polyelectrolyte and a cationic surfactant. It is preferred to use cationic polyelectrolytes and anionic surfactants.
The stoichiometry of the complex, based on the charges of polyelectrolyte and surfactant, is preferably such that there is essentially charge compensation in respect of the polyelectrolyte on the one side and surfactant on the other. Advantageously, therefore, the stoichiometry of the complex, based on the charges of polyelectrolyte and surfactant, is from about 1.5:1 to 1:1.5, with particular preference from about 1.3:1 to 1:1.3, and most preferably about 1:1.
In addition, the complex preferably has a mesomorphic structure, as may be determined by measuring the small-angle X-ray scattering. It is further preferable that the complexes of the invention possess no crystallinity, as can be determined by measuring the wide-angle X-ray scattering.
The complexes of the invention are obtainable by adding an aqueous solution of the polyelectrolyte to an aqueous solution of the fluorinated surfactant and isolating the resultant precipitate, which forms spontaneously. Both when adding a cationic polyelectrolyte in aqueous solution to an aqueous solution of the anionic fluorinated surfactant, and when adding an anionic polyelectrolyte to a cationic fluorinated surfactant, the complex preferred in accordance with the invention is formed with a stoichiometry of about 1:1, based on the charges of polyelectrolyte and surfactant. Moreover, the formation of this preferred complex is favored by working at an elevated temperature of at least 40xc2x0 C., with particular preference from 50 to 90xc2x0 C. In the converse casexe2x80x94the addition of a surfactant solution to the polyelectrolyte solutionxe2x80x94it is not unusual for there to be considerable deviations from the preferred stoichiometry, which in certain instances may result in an unwanted sharp increase in the hygroscopicity.
The resultant novel supramolecular polymer complex precipitate may be dissolved in polar organic solvents. This is surprising, since polymeric materials having a high fluorine content are usually of extremely low solubility or else completely insoluble. When this complex solution is applied to a surface and the solvent is evaporated, a thin, usually transparent film of the complex material is formed on the surface. It has been found that the surface energy after coating with the complex materials of the invention was lower in all cases than prior to coating. A consequence of this is reduced adhesion of impurities on the surface. This effect was found on a large number of different surfaces, examples being glass, stone, wood, paper, metal, plastics, natural materials such as cotton fibers, for instance, and on painted surfaces as well; in other words, the effect is independent of the type of substrate and is accompanied by good coating adhesion.
A further surprising finding has been that the complexes of the invention are readily emulsifiable with nonionic surfactants, preferably nonionic fluorinated surfactants. In this way, the complexes may also be processed with an aqueous carrier material and hence applied in a particularly environment-friendly way.
The present invention therefore further provides a complex comprising polyelectrolyte and ionic fluorinated surfactant, said complex further comprising at least one nonionic surfactant, preferably a nonionic fluorinated surfactant. The proportion of the nonionic surfactant may be varied over a wide range depending on the nature of the application and may, for example, be up to 200% (w/w) based on the weight of the complex.
By varying the proportion of emulsifier, i.e., nonionic surfactant, it is possible to control the permanence of the coating. For the application of permanent coatings, the proportion of the nonionic surfactant should be up to not more than 20%, preferably up to 10% and, with particular preference, up to 5%, based in each case on the weight of the complex. For temporary coatings, proportions of the nonionic surfactant of from 20 to 200% and, in particular, from 50 to 80%, based on the weight of the complex, are preferred. With a high proportion of emulsifier, the coating may be washed off using customary domestic surfactant solutions. This is of great interest in particular for the temporary intransit coating of, say, automobiles.
It has been found, furthermore, that the gas permeability and water absorption capacity may both be varied widely by means of appropriate combinations of polyelectrolyte and surfactant. This is of great importance since with many coatings, such as antigraffiti coats, for example, it is necessary not to seal the surfaces, in order to prevent the formation of mold and fungus.
The complex compounds of the invention can be prepared easily and quickly, from aqueous solution, for example.
They can be processed both as solutions and as aqueous emulsions to form thin films on any desired surfaces. For very low expenditure of material, these films greatly reduce the surface energy, and so can be used almost universally wherever surfaces having Teflon-like properties are required or desired.
Owing to the low coat thicknesses required to reduce the surface energy, the ease of preparation, and the short drying times, the coating is very cost-effective per unit area. The drying times of the films may be reduced to a few minutes or hours. The coating permits elastic flexing of the coated articles. The film coatings are preferably transparent and are impossible or difficult to perceive under light which is incident, for example, at an oblique angle. The breathability, i.e., the permeability to gases and water vapor, and also water absorption, can be adjusted within wide limits.
The coating of surfaces with the polyelectrolyte-fluoro surfactant complexes of the invention is always judicious when the aim is to reduce natural or artificial soiling. For this purpose the surface is coated with a thin film. Irrespective of the nature of the surface, the surface energy is reduced as a result of the coating. The coating permits elastic flexing of the coated article without chipping or flaking. The films possess long-term stability at temperatures of up to 100xc2x0 C. Depending on the complex used, temperature stabilities of from 120 up to 230xc2x0 C. may even be attained.
With the exception of highly hygroscopic polyelectrolytes such as polyacrylic acid, polymethacrylic acid and poly(diallyldimethylammonium chloride), and salts thereof, any desired combinations of polyelectrolytes and fluorinated ionic surfactants are suitable. When using nonhygroscopic polyelectrolytes of the invention, the complexes obtained have a low water absorption of preferably not more than 5% (w/w), with particular preference not more than 4.5% (w/w), and most preferably not more than 4% (w/w), based on the weight of the complex, at 20xc2x0 C. and 100% relative atmospheric humidity.
Polyelectrolytes are substances containing two or more positive or negative charge carriers. A preferred class of cationic polyelectrolytes are polymers containing preferably at least 20% of one or more of the following monomer units, with the proviso that the resultant polyelectrolyte is a nonhygroscopic polyelectrolyte within the meaning of the present invention:
ethylenically unsaturated monomers which carry positively charged nitrogen groups, e.g., quaternary ammonium groups or N-substituted heteroaromatic groups, said monomers being in the form either of salts, as obtained by reacting basic amino functions with mineral acids, e.g., hydrochloric acid, sulfuric acid or nitric acid, or in quaternized form (e.g., by reaction with dialkyl sulfates such as dimethyl sulfate, diethyl sulfate, etc., alkyl chlorides such as methyl chloride, ethyl chloride, etc., or benzyl chloride), examples being dimethylaminoethyl acrylate hydrochloride, diallyldimethylammonium chloride, dimethylaminoethyl acrylate methosulface, di-methylaminopropylmethacrylamide methochloride, di-methylaminopropylmethacrylamide methosulfate, vinylpyridinium salts, and 1-vinylimidazolium salts.
In addition to the cationic monomer units, the cationic polyelectrolyte may if desired contain one or more nonionic monomers in an amount, for example, of up to 80 mol %. The presence of nonionic monomers is necessary in some instances, as in the case of poly(diallyldimethylammonium chloride), for example, in order to reduce the hygroscopicity.
Examples of suitable nonionic monomers are C1 to C20 alkyl esters and hydroxyalkyl esters, and especially amides and N-substituted amides, of monoethylenically unsaturated C3 to C10 monocarboxylic acids or C4 to C8 dicarboxylic acids, e.g., acrylamide, methacrylamide, N-alkylacrylamides or N,N-dialkylacrylamides having in each case 1 to 18 carbon atoms in the alkyl group, such as N-methylacrylamide, N,N-dimethylacrylamide, N-tert-butylacrylamide or N-octadecylacrylamide, N-methylhexylmaleimide, N-decylmaleimide, dimethylaminopropylmethacrylamide or acrylamidoglycolic acid, and also alkylaminoalkyl (meth)acrylates, examples being di-methylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminoechyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylate and di-methylaminopropyl methacrylate, and also vinyl esters, examples being vinyl formate, vinyl acetate and vinyl propionate, which after polymerization may also be present in hydrolyzed form, and also N-vinyl compounds, examples being N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, N-vinyl-N-methylformamide, 1-vinylimidazole, 1vinyl-2-methylimidazole, and N-methylvinylacetamide.
An example of cationic polyelectrolytes composed of cationic and nonionic monomers is as follows:
copolymers of dialkenyldialkylanmonium salts, e.g., diallyldimethylammonium chloride, with nonionic monomers, e.g., N-methylvinylacetamide, in which the proportion of nonionic monomer is preferably at least 20 mol %.
Further preferred classes of cationic polyelectrolytes are the following:
polyethyleneimines and alkyl-substituted polyethyleneimines, e.g., poly(ethyleneimine-co-N-docosylethylimine);
ionenes, i.e., polymers having two or more quaternary ammonium groups and formed, for example, by reacting di-tertiary amines with xcex1,xcfx89-dihaloalkenes, e.g., 6,3-ionene, and
polysaccharides containing cationic groups, especially xcex2-glycosidically linked polysaccharidea, such as chitosan, for instance.
To prepare the complexes of the invention, said cationic polyelectrolytes can be used in base form, partially neutralized or tully neutralized.
In addition, anionic polyelectrolytes are also suitable for the method of the invention. A preferred class of such anionic polyelectrolytes are polymers containing preferably at least 20 mol % of one or more of the following monomer units, with the proviso that the resultant polyelectrolyte is a nonhygroscopic polyelectrolyte within the meaning of the present invention:
ethylenically unsaturated carboxylic acids and their salts and derivatives, e.g., C3 to c10 mono-carboxylic acids, their alkali metal and/or ammonium salts, examples being dimethylacrylic acid or ethylacrylic acid, C4 to C8 dicarboxylic acids, their monoesters, anhydrides, alkali metal salts and/or ammonium salts, e.g., maleic acid, fumaric acid, itaconic acid, mesaconic acid, methylenemalonic acid, citraconic acid, maleic anhydride, itaconic anhydride or methylmalonic anhydride;
ethylenically unsaturated monomers containing sulfonic acid groups, examples being allylsulfonic acid, styrenesulfonic acid, vinylsulfonic acid, 3-sulfopropyl acrylate, and 3-sulfopropyl methacrylate,
monoethylenically unsaturated monomers containing phosphinic, phosphonic or phosphoric acid groups, e.g., vinylphosphonic acid, allylphosphonic acid, or acrylamidomethylpropanephosphonic acid.
If desired, these anionic polymers may contain one or more of the abovementioned nonionic monomers in a proportion, for example, of up to 80 mol %. The use of copolymers comprising anionic and nonionic monomers is preferred for some of the anionic monomers in order to reduce the hygroscopicity.
A further preferred class of anionic polyelectrolytes are polyaaccharides containing anionic groups.
The anionic polyelectrolytes can be used in the acid form, partially neutralized or fully neutralized.
Ionic fluorinated surfactants are substances which contain at least one fluorine atom attached to a carbon atom, preferably at least one xe2x80x94CF2 group and/or CF3 group, and at least one charge carrier.
Anionic fluorinated surfactants comprise at least one fluorine-containing hydrophobic group and at least one negative charge carrier. Examples of such compounds are fluorinated carboxylic acids and their salts with organic or inorganic cations, fluorinated sulfonic acids and their salts with organic or inorganic cations, fluorinated organic sulfuric acids and their salts with organic or inorganic cations, and fluorinated phosphinic, phosphonic or organ-phosphoric acids and their salts with organic or inorganic cations.
Among these classes of compound, preference is given to the following;
perfluorocarboxylic acids and their preferably water-soluble salts, such as perfluoroalkanoic acids, e.g., in particular, perfluoroalkanoic acids of the formula CF3(CF2)nxe2x80x94COOH, where n is preferablyxe2x89xa77;
partially fluorinated carboxylic acids and carboxylic acid salts, such as partially fluorinated alkanoic acids, partially fluorinated alkenoic acids, perfluoroalkoxyalkanoic acids, perfluoroalkylethyleneoxyalkanoic acids, perfluoroalkoxybenzoic acids, and partially fluorinated carboxylic acids containing sulfide, sulfone, carboxamide, hydroxyl, oxo and/or ether groups, and salts of such acids; e.g., lithium 3-[(1H, 1H, 2H, 2H-fluoroalkyl) thio]propionate, Zonyl FSA(copyright), Du Pont;
perfluorosulfonic acids and their preferably water-soluble salts, such as perfluoroalkanesulfonic acids of the formula CF3(CF2)mxe2x80x94SO3H, where mxe2x89xa71;
partially fluorinated sulfonic acids and their preferably water-soluble salts, such as partially fluorinated alkanesulfonic acids, e.g., perfluoroalkylethaniesulfonic acids, perfluoropropylalkanesulfonic acids, partially fluorinated arylsulfonic acids, e.g., perfluoroalkylbenzenesulfonic acids, perfluoroalkoxybenzenesulfonic acids, perfluoroacylbenzenesulfonic acids, partially fluorinated alkenesulfonic acids, and also partially fluorinated sulfonic acids containing sulfide, carboxamide, hydroxyl, oxo and/or ether groups, fluorinated sulfo esters, e.g., sulfosuccinic esters, perfluoroalkyl sulfopropionates, perfluoroalkyl sulfobutyrates and salts thereof; e.g. perfluoroalkylethylsulfonic acid ammonium salt, Zonyl TBS(copyright) Du Pont; sodium [succinic acid diperfluoroalkylethyl diester 2-sultonate], Fluowet SB(copyright), Hoechst;
fluorinated organic sulfuric acids and their salts, such as perfluoroalkylated methyl sulfates, fluorinated sulfatopoly(oxyethylene), perfluoropropoxylated sulfates, and salts thereof;
fluorinated phosphinic and phosphonic acids and their preferably water-soluble salts, e.g., Fluowet PL80(copyright), Hoechst;
fluorinated organic phosphoric acids and their salts, such as perfluoroalkylethanephosphoric acids, mono- and bis(fluoroalkyl)phosphoric acids, perfluoroalkylphosphoric acids, fluorinated alkene-phosphoric acids, fluorinated phosphate alkyl esters, e.g., phosphoric acid perfluoroalkyl ester ammonium salt, Zonyl FSE(copyright) and Zonyl FSP(copyright), Du Pont.
Cationic surfactants are also suitable for the method of the invention. Preferred classes of such compounds are as follows:
fluorinated amines and ammonium salts, such as fluoroalkylammonium salts, which may if desired contain carboxamide, sulfonamide, sulfide, ester and/or hydroxyl groups, or heterocyclic nitrogen compounds, e.g., perfluoroalkylethyltrialkylammonium methosulfate, Hoe-L-3658-1, Hoechst.
Examples of nonionic surfactants, especially fluorinated surfactants, are compounds containing one or more nonionic hydrophilic groups and one or more fluorine-containing hydrophobic groups. Preferred examples of such compounds are fluorinated alcohols, examples being those containing one or more oxyethylene or oxypropylene groups, fluorinated polyethers, fluorinated polyhydric alcohols, oxyalkylated perfluorophenols, perfluoroalkyl-2-ethanethiol derivatives, and also compounds containing carboxamide or sulfonamide groups.
Further judicious ionic fluorinated surfactants that can be used to prepare the complexes, and nonionic fluorinated surfactants that can be used as emulsifiers to prepare aqueous emulsions, are described in the book by Erik Kissa (Fluorinated Surfactants, Surfactant Science Series Vol. 50, Marcel Dekker, Inc., New York, 1994)
Complexes of the invention further comprising a nonionic surfactant are preferably prepared by adding the particular desired proportion of nonionic surfactant to a complex comprising polyelectrolyte and fluorinated ionic surfactant.
The present invention further provides a formulation comprising a complex of the invention, comprising polyelectrolyte and ionic fluorinated surfactant, in solution in a polar organic solvent. Said formulation comprises the complex preferably in a proportion of from 0.1 to 30% (w/w), with particular preference from 0.5 to 10% (w/w), and most preferably from 1 to 5% (w/w), based on the weight of the formulation. The solvent is preferably a volatile and largely nontoxic organic solvent, examples being methanol, ethanol, acetone, ethyl acetate, and mixtures thereof.
The present invention additionally provides a formulation comprising a complex of the invention, comprising polyelectrolyte and ionic fluorinated surfactant, and preferably nonionic surfactant, in emulsion in an aqueous solvent. The complex is present preferably in a proportion of from 0.1 to 30% (w/w), with particular preference from 0.5 to 10% (w/w), and most preferably from 1 to 5% (w/w), based on the weight of the emulsion. The emulsion of the invention is, surprisingly, stable at 20xc2x0 C. for at least two weeks.
The emulsion of the invention is obtainable by adding the particular desired amount of a nonionic surfactant to a complex comprising polyelectrolyte and ionic fluorinated surfactant, converting this mixture into a substantially homogeneous mixture, and diluting that mixture with water, preferably in portions, so as to obtain an aqueous emulsion.
The complexes of the invention, and the complex-containing compositions, might be used to coat surfaces. Exemplary applications are as antisoiling compositions, especially antigraffiti compositions, as protective compositions for vehicles in transit, e.g., automobiles or machines, as anti-icing protection, especially for civilian or military air travel, as marine antifouling coatings, as release agents and lubricants, in the production, for example, of tiles, bricks or construction shuttering, as compositions for impregnating textiles, e.g., cotton with GoreTex properties, and carpeting, and as a membrane, e.g., as a gas separation membrane.
The invention further provides a method of coating a surface, in which a formulation of the invention is applied to said surface and allowed to dry. This coating operation mayxe2x80x94where necessaryxe2x80x94also be repeated, using different complexes in each case if desired. Application may be made from an organic solution or from an aqueous emulsion. The drying time for organic solutions is preferably not more than 1 hour, with particular preference from a few seconds to a few minutes. The drying time for aqueous emulsions is preferably not more than 6 hours, with particular preference not more than 3 hours. The coating composition may be applied discontinuously or continuously by means of customary techniques such as, for instance, spraying, flow coating, dipping, or mechanical application, e.g., roller application. The thickness of the coating is preferably from 0.1 xcexcm to 1 mm, with particular preference from 1 to 10 xcexcm.
The present invention provides, further still, an article coated at least in part with a coating comprising a complex of the invention comprising polyelectrolyte and fluorinated ionic surfactant. The coated surface preferably has an energy of less than 20 mN/m. The coating is preferably substantially transparent, ie., transparent to visible light. Further, the coating is preferably stable to contact with a water-containing atmosphere; that is, it does not tend toward significant swelling. Furthermore, the coating is preferably stable up to a temperature of 100xc2x0 C. Depending on what is required, the coating may be permanent or temporary, permeable to air and/or moisture, or impermeable to air and/or moisture.
One advantage of the coatings of the invention is that at their surface facing the surroundings they have a heightened fluorine content as compared with the interior of the coating, a fact which contributes to reducing the surface energy. Furthermore, they possess preferably a contact angle hysteresis of between 5xc2x0 and 20xc2x0. In addition, the coatings of the invention exhibit low water absorption, preferably not more than 5% (w/w), with particular preference not more than 4.5% (w/w), and most preferably not more than 4% (w/w), based on the weight of the coating, at 20xc2x0 C. and 100% relative atmospheric humidity.